How to Create Subset Fonts in .NET?

Question

I have a Silverlight application that I need to embed some less-than-common fonts in. It\'s simple enough for me to just copy over the TTF/OTF and compile that with my app.

Answer 1

I know it's an old question but I found very difficult to use the CreateFontPackage API from C# (as mentioned by @josh3736's answer) so I thought to share my code.

I'm using the API with the glyphIndices, you can use it directly with the characters by removing the TTFCFP_FLAGS_GLYPHLIST flag.

This is my code:

public byte[] CreateSubset(byte[] inputData, IEnumerable glyphIndices)
{
    AllocProc allocProc = Marshal.AllocHGlobal;
    ReallocProc reallocProc = (p, c) =>
        p == IntPtr.Zero
            ? Marshal.AllocHGlobal(c)
            : Marshal.ReAllocHGlobal(p, c);
    FreeProc freeProc = Marshal.FreeHGlobal;

    var resultCode = CreateFontPackage(
        inputData, (uint) inputData.Length,
        out var bufferPtr,
        out _,
        out var bytesWritten,
        TTFCFP_FLAGS_SUBSET | TTFCFP_FLAGS_GLYPHLIST,
        0,
        TTFMFP_SUBSET,
        0,
        TTFCFP_MS_PLATFORMID,
        TTFCFP_UNICODE_CHAR_SET,
        glyphIndices,
        (ushort)glyphIndices.Length,
        allocProc, reallocProc, freeProc, (IntPtr)0);

    if (resultCode != 0 || bufferPtr == IntPtr.Zero)
    {
        return null;
    }

    try
    {
        var buffer = new byte[bytesWritten];
        Marshal.Copy(bufferPtr, buffer, 0, buffer.Length);
        return buffer;
    }
    finally
    {
        freeProc(bufferPtr);
    }
}

internal const ushort TTFCFP_FLAGS_SUBSET = 0x0001;
internal const ushort TTFCFP_FLAGS_COMPRESS = 0x0002;
internal const ushort TTFCFP_FLAGS_TTC = 0x0004;
internal const ushort TTFCFP_FLAGS_GLYPHLIST = 0x0008;

internal const ushort TTFMFP_SUBSET = 0x0000;

internal const ushort TTFCFP_UNICODE_PLATFORMID = 0x0000;
internal const ushort TTFCFP_MS_PLATFORMID = 0x0003;

internal const ushort TTFCFP_UNICODE_CHAR_SET = 0x0001;

[UnmanagedFunctionPointer(CallingConvention.Cdecl, CharSet = CharSet.Unicode)]
private delegate IntPtr AllocProc(Int32 size);

[UnmanagedFunctionPointer(CallingConvention.Cdecl, CharSet = CharSet.Unicode)]
private delegate IntPtr ReallocProc(IntPtr memBlock, IntPtr size);

[UnmanagedFunctionPointer(CallingConvention.Cdecl, CharSet = CharSet.Unicode)]
private delegate void FreeProc(IntPtr memBlock);

[DllImport("FontSub.dll", CallingConvention = CallingConvention.Cdecl, CharSet = CharSet.Ansi, ExactSpelling = true)]
private static extern uint CreateFontPackage(
    [In, MarshalAs(UnmanagedType.LPArray, SizeParamIndex = 1)]
    byte[] puchSrcBuffer,
    uint ulSrcBufferSize,
    out IntPtr puchFontPackageBufferPtr,
    out uint pulFontPackageBufferSize,
    out uint pulBytesWritten,
    ushort usFlags,
    ushort usTtcIndex,
    ushort usSubsetFormat,
    ushort usSubsetLanguage,
    ushort usSubsetPlatform,
    ushort usSubsetEncoding,
    [In, MarshalAs(UnmanagedType.LPArray, SizeParamIndex = 12)]
    ushort[] pusSubsetKeepList,
    ushort usSubsetKeepListCount,
    AllocProc lpfnAllocate,
    ReallocProc lpfnReAllocate,
    FreeProc lpfnFree,
    IntPtr lpvReserved
);

I used with code only with TTF files, for TTC (font collections) you have to change a few things but it should work nonetheless.